Infrared spectroscopy apparatus

ABSTRACT

This invention relates to apparatus for use in isolating monomers of hydrogen-bonded organic compounds, liquids or solids at room temperature in a low temperature inert gas matrix. The apparatus comprises a refrigerated section having an infrared window, a second refrigerated section for pre-cooling the inert matrix gas and for receiving vaporized material to be deposited on the infrared window, the second section having matrix gas nozzles adjacent to a resistance heated sample inserting nozzle entering the second section from an adjacent sample heating and valving section. The nozzle is coupled to a sealed sample container which is inserted in an electrically heated furnace disposed within the second section.

United States Patent [1 1 King [54] INFRARED SPECTROSCOPY APPARATUS [75]Inventor: Stanley T. King, Midland, Mich.

[73] Assignee: The Dow Chemical Company,

Midland, Mich.

[22] Filed: Nov. 3, 1970 211 Appl. No.: 195,439

[52] U.S. Cl ..118/48, 118/69, 250/833 11,

356/38 [51] Int. Cl ..C23c 13/12 [58] Field of Search ..l 18/48-495, 5,69, 9;

250/833 H, 43.5 R v 8/1969 Beattie ..356/37 UX 9/1970 Webb ..1l8/9XPrimary Examiner-Morris Kaplan Attorney-William M. Yates and Earl D.Ayers [57] ABSTRACT This invention relates to apparatus for use inisolating monomers of hydrogen-bonded organic compounds, liquids orsolids at room temperature in a low temperature inert gas matrix. Theapparatus comprises a refrigerated section having an infrared window, asecond refrigerated section for pie-cooling the inert matrix gas and forreceiving vaporized material to be deposited on the infrared window, thesecond section having matrix gas nozzles adjacent to a resistance heatedsample inserting nozzle entering the second section from an adjacentsample heating and valving section. The nozzle is coupled to a sealedsample container which is inserted in an electrically heated furnacedisposed within the second section.

[56] References Cited UNITED STATES PATENTS 2,847,319 8/1958 Marvin..118/49 X 3,055,775 9/1962 Crittenden, Jr. et a1 ..l18/49 XPATENTEDNAYZZ ma 3, 734, 056

sum 1 OF 2 1 INFRARED SPECTROSCOPY APPARATUS BACKGROUND OF THE INVENTIONThis invention relates to apparatus for use in infrared spectroscopy andparticularly to a matrix isolation device for use in studyinghydrogen-bonded, high-boiling organic compounds by infraredspectroscopy. Low temperature matrix isolation techniques have been usedby infrared spectroscopists for more than ten years in the study oflow-boiling compounds, unstable molecular species and very high-boilinginorganic compounds. However, little information can be found in theliterature about the matrix isolation of the strongly hy drogen-bondedsolid organic compounds for analytical studies.

It is well-known to spectroscopists that molecules with OH or NH groupsare usually intermolecularly bonded in the liquid or solid phases andthe -H or NH stretching absorption band is broad in the infraredspectrum. It is difficult to interpret this broad band into usefulchemical information. On the other hand, the unassociated OH group showsa sharp absorption in the region 38003500 cm and the unassociated NHgroup shows a sharp absorption in the region 3600-3200 cm and thefrequency at which this band absorbs enables specific identification ofthe particular group present in the molecule. Infrared spectra ofunassociated species of molecules containing the NH or OH group can beobtained in dilute solution, but the molecule must be soluble in asuitable solvent which does not mask the 11 or 11 absorption bands orother bands. Moreover, many compounds are not soluble in a suitablesolvent, and the spectra of their unassociated species cannot be studiedin this manner.

Thermal disassociation of hydrogen-bonding in the gas phase is anotherway to obtain the infrared spectrum of the monomeric species, but forsolid sample with very low vapor pressure, a good vapor spectrum is verydifficult to obtain. In addition, the overlapping of the broad bands ingas phase spectrum makes it difficult to distinguish them. The spectrumof the monomeric species isolated in low temperature matrix can avoidall the problems discussed above.

Generally, the unassociated species, which can be obtained either bythermal dissociation or by dilution in gas phase, are frozen in a largeamount of inert gas matrix on a cold window surface (at 6 or 20 K.) isimpractical for a solid sample with negligible vapor pressure at roomtemperature. Therefore, thermal dissociation has to be used in thiscase. Usually the hot, unassociated sample in the vapor phase isdeposited on the cold window separately with the pre-cooled matrix gasthrough two different nozzles. Otherwise, the deposition of thepre-mixed hot sample with a large amount of hot matrix gas will cause aninstantaneous temperature increase on the cold window surface and poorresults of the isolation may be obtained.

Accordingly, a principal object of this invention is to provide animproved device for use in isolating monomers of hydrogen-bonded organiccompounds, liquids or solids at room temperature in a low temperatureinert gas matrix.

Another object of this invention is to provide an improved, fasteroperating and easier to use device for use in isolating monomers ofhydrogen-bonded organic compounds, liquids, or solids at roomtemperature in a low temperature inert gas matrix.

In accordance with this invention there is provided matrix isolationapparatus comprising a refrigerated section which includes a rotatableso called infrared window on which the material to be analyzed isdeposited, a section for pre-cooling the matrix gas and having nozzleslocated on each side of a sample thin walled nozzle which is insertedinto that section from an adjacent sample valving and heating section.The sample nozzle functions as a resistance heating element to preventcooling of the sample before it leaves the nozzle, preventing settlingof the sample material on the nozzle wall. The nozzle is coupled to anenclosed sample capsule which is inserted within a heating oven in theprecooling section.

The invention, as well as additional objects and advantages thereof,will best be understood when the following detailed description is readin connection with the accompanying drawing, in which:

FIG. 1 is a diagrammatical view, partly broken away and in section, ofapparatus in accordance with the invention,

FIG. 2 is an enlarged view of the sample holder and nozzle of theapparatus of FIG. 1;

FIG. 3 is an enlarged side elevational view, in section, of the samplecell heating oven, and

FIG. 4 is a sectional view taken along the line 4-4 of FIG. 3.

Referring to the drawing, and particularly to FIG. 1, there is shownmatrix isolation apparatus, indicated generally by the numeral 10. Theapparatus 10 comprises a first refrigerated compartment 16 havingdispersed therein a heat-exchanger 14 containing liquid hydrogen, liquidhelium, or both. A so-called infrared window 12, composed of a crystalof sodium chloride, potassium bromide of cesium iodide, for example, ina metal (copper, for example) frame is mechanically and thermallycoupled to the lower end part of the heat exchanger 14. A radiationshielding structure 18 surrounds the heat exchanger.

A second section, comprising a compartment 48 having a vacuum containersuch as a Dewar container 38 coupled to it, is coupled to thecompartment 16 near the lower end thereof by means of a mounting flange50.

The container 38 contains liquid nitrogen and a coil 40 through whichthe matrix gas (argon, for example) pre-cooled by the liquid nitrogen,is to be introduced to the chamber 48 through nozzles 42, 44 which arecoupled to the lower part of the coil 40.

Referring to FIGS. 2, 3 and 4, as well as to FIG. 1, a sample inputnozzle, indicated generally by the numeral 22, is coupled and sealed tothe end of a bushing 20 which closes the open end of the tubular samplecontainer 26. The container 26 is generally of U- shaped longitudinalcross sectional configuration.

The nozzle 22 has electrical leads (usually nichrome wires) 28, 30coupled to its outer end and to the'bushing 20, respectively, as bysilver soldering. The sample cell heating oven 32 is an elongated memberhaving intemal and external cup-like wall and end parts 32, 34respectively. A heating coil 56, disposed between the internal andexternal walls, is separated from the metal walls by sheets 58, 68 ofinsulating material such as mica, for example.

A thermocouple 70 is disposed in the oven 32 near the bottom of theinner wall structure, its leads extending through the closed end of theoven. The oven 32 is supported by a bracket 60 which is rigidly securedat its flanged end 62 to closure plate 64 which is sealed to the outerend of compartment 48. Feed through elements 66, 72 couple theelectrical leads 30, 28, respectively, through the plate 64. Closuretube 74, coupled to the plate 64, permits air-tight feed through of thethermocouple and heater leads 76, 78, respectively. The seal between theplate 64 and the end of the compartment 48 may be made by O-rings or anysuitable means.

In operation, the sample material is inserted in the sample holder 26bushing sealed at the open end of the holder. The holder 26 is theninserted in the oven with the closed end of the holder touching oralmost touching the thermocouple 70. The plate 64 is then sealed to theouter end of compartment 48 and compartments 16 and 48 are evacuated.The oven is then heated to vaporize the sample in the holder at acontrolled rate.

The nozzle 22 is maintained at a higher temperature (60500 C., forexample) by passing electric current through it than the temperature inthe oven 32 so as to ensure disassociation of the hydrogen bondmolecules and also to prevent any deposition of the sample on the nozzle22. It is very important to keep the sampling device free from sampledeposition for routine analysis use because otherwise the impurity fromthe previous sample would obscure the spectrum of a new sample.

The temperature of the window 12 is reduced by the heat exchanger to atemperature of 20 Kelvin operating with liquid hydrogen or to 6 Kelvinoperating with hydrogen and helium gases.

The sample vapor and matrix gas from the nozzles 42, 44 are directed tothe window 12 where the sample material is frozen in the matrix gas. Thewindow 12 is then rotated 90 so the window may be aligned with respectto the infrared beam in the spectrometer (not shown) and the spectrumrecorded.

After the deposition is finished and the spectrum is recorded, the leads28, are de-energized, the heater in the oven 32 is turned off to coolit, and the plate 64 removed from the compartment 48. The sample holder26 and nozzle 22, after uncoupling the electrical leads 28, 30, may thenbe removed and another sample holder and nozzle assembly inserted in theoven. The electrical leads 28, 30 are then re-connected and the plate 64is ready to be re-sealed to the compartment 48 and the apparatus may beevacuated.

In the apparatus shown a gold O-ring is used to provide a gas tight sealbetween the bushing 20 and the body of the sample holder 26. Normally aViton O-ring seal is provided between the plate 64 and the compartment28. The inner and outer wall structure of the oven 32 are made ofstainless steel, as is the nozzle tube 22.

The electrical leads 28, 30 are usually nichrome and sized to be heatedto about the same temperature as the temperature of the nozzle 22 whencurrent is applied thereto.

A brass plate 80, disposed adjacent to the entry into the compartment12, with the nozzles 22, 42 and 44 extended through or past itssections, provides a baffle to minimize heat transfer from the sampleholder and oven into the compartment 12.

Excellent results were obtained when urea, acetamide, cyanamide,chlorinated 2 pyridinols and 3,4- dichloro-2,6-dimethyl-4-pyridinol wereused as sample materials.

The apparatus of the invention is helpful also from an operationalstandpoint because sample holders and nozzles may be easily cleaned andreinserted in the heating assembly. Further, the nozzle may be heatedover a wide temperature range since no insulated coil winding is presentin the nozzle.

What is claimed is:

1. In analytical apparatus comprising an evacuated chamber having a heatexchanger therein which has an infrared window physically and thermallycoupled thereto, a means for directing a pre-cooled matrix gas towardssaid window, means for heating a sample to be analyzed, and meansincluding a walled nozzle extending into said chamber for directingheated sample to be analyzed towards said window, the improvementcomprising providing a sealed sample holder adapted to be inserted intosaid means for heating the sample to be analyzed, said sample holderhaving said nozzle coupled thereto, the nozzle having thin walls whichfunction as an electrical heater, and means for electrically energizingsaid nozzle across the ends thereof.

2. Apparatus in accordance with claim 1, wherein said nozzle is a thinwalled stainless steel tube.

3. Apparatus in accordance with claim 1, wherein said means for heatingsaid sample is a temperature controllable resistance heating ovendisposed within said evacuated chamber.

4. Apparatus in accordance with claim 2, wherein said sample holder is atubular element having an open end and a closed end, said open end beingclosed with a cap having said nozzle sealed thereto, said holder beingadapted to fit closely but slidably in said means for heating.

5. Apparatus in accordance with claim 1, wherein heat baffle means areprovided between said means for heating and the end'of said nozzle.

6. Apparatus in accordance with claim 5, wherein said baffle means is aplate-like structure which is cooled by said pre-cooled matrix gas andby conduction to a heat sink.

@333 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION May 22, 1973Patent No- 3 .734 056 Dated inventofls) si-anlev '1. King It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 4, line 11, delete "3,4- and insert 3,5-

Signed and sealed this 12th day of-Pehruary 1974.

(SEAL) Attest:

EDWARD M. FLETCHERJR. c MARSHALL DANN A testlng Offlcer Commissioner ofPatents

1. In analytical apparatus comprising an evacuated chamber having a heatexchanger therein which has an infrared window physically and thermallycoupled thereto, a means for directing a pre-cooled Matrix gas towardssaid window, means for heating a sample to be analyzed, and meansincluding a walled nozzle extending into said chamber for directingheated sample to be analyzed towards said window, the improvementcomprising providing a sealed sample holder adapted to be inserted intosaid means for heating the sample to be analyzed, said sample holderhaving said nozzle coupled thereto, the nozzle having thin walls whichfunction as an electrical heater, and means for electrically energizingsaid nozzle across the ends thereof.
 2. Apparatus in accordance withclaim 1, wherein said nozzle is a thin walled stainless steel tube. 3.Apparatus in accordance with claim 1, wherein said means for heatingsaid sample is a temperature controllable resistance heating ovendisposed within said evacuated chamber.
 4. Apparatus in accordance withclaim 2, wherein said sample holder is a tubular element having an openend and a closed end, said open end being closed with a cap having saidnozzle sealed thereto, said holder being adapted to fit closely butslidably in said means for heating.
 5. Apparatus in accordance withclaim 1, wherein heat baffle means are provided between said means forheating and the end of said nozzle.
 6. Apparatus in accordance withclaim 5, wherein said baffle means is a plate-like structure which iscooled by said pre-cooled matrix gas and by conduction to a heat sink.